External Coil Assembly for Implantable Medical Prostheses

ABSTRACT

Methods and devices for inductively coupled implants on the human or animal body are disclosed. An external coil assembly to be used with the implant has a transmitting coil and one or more receiving coils. The number of the receiving coils, their distance from the transmitting coil and their shape is chosen to reduce the influence of a noise signal received by the external coil assembly.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/529,809,entitled “External Coil Assembly for Implantable Medical Prostheses”,filed Sep. 29, 2006. The present invention is related to U.S. Pub. App.No. 2005/0222624 (Retinal Prosthesis with Side Mounted Inductive Coil)and U.S. Pub. App. No. 2005/0288734 (Visuai Prosthesis with OperationalData Telemetry), the disclosures of both of which are incorporatedherein by reference in their entirety.

FEDERALLY SPONSORED RESEARCH

This invention was made with government Support under grant no.R24EY12893-01, awarded by the National Institutes of Health. The U.S.Government has certain rights in the invention.

BACKGROUND

1. Field

The present disclosure relates to devices implantable on the animal orhuman body. In particular, it relates to an external coil assembly forimplantable medical prostheses.

2. Related Art

In inductively powered retinal prostheses, coils are used to transmitand receive RF power in both external and implant ends. Reference can bemade, for example, to U.S. Pat. No. 5,935,155 (Visual Prosthesis andMethod of Using Same), incorporated herein by reference in its entirety.Due to the low power nature of the implant device and the limitedimplant coil size, it imposes difficulties to retrieve the low levelfeedback signals at the external side in the presence of a strongmagnetic field created by the external transmitting power carrier. Thisis especially true when the back telemetry signal frequency is not muchfar away from the power carrier. In the case of retinal prosthesis whenthe implant coil is mechanically linked to the eyeball, the eyeballmovement compromises the coupling condition between the external andimplant coils and therefore makes the back telemetry signal condition atthe external receiving end worse. There is a need for an apparatus andmethod to reduce and possibly minimize the power carrier component inthe received spectrum and therefore to improve the back telemetryreliability.

In 1755 LeRoy passed the discharge of a Leyden jar through the orbit ofa man who was blind from cataract and the patient saw “flames passingrapidly downwards.” Ever since, there has been a fascination withelectrically elicited visual perception. The general concept ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising a prosthesis foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthetic devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

In the early 1930's, Foerster investigated the effect of electricallystimulating the exposed occipital pole of one cerebral hemisphere. Hefound that, when a point at the extreme occipital pole was stimulated,the patient perceived a small spot of light directly in front andmotionless (a phosphene). Subsequently, Brindley and Lewin (1968)thoroughly studied electrical stimulation of the human occipital(visual) cortex. By varying the stimulation parameters, theseinvestigators described in detail the location of the phosphenesproduced relative to the specific region of the occipital cortexstimulated. These experiments demonstrated: (1) the consistent shape andposition of phosphenes; (2) that increased stimulation pulse durationmade phosphenes brighter; and (3) that there was no detectableinteraction between neighboring electrodes which were as close as 2.4 mmapart.

As intraocular surgical techniques have advanced, it has become possibleto apply stimulation on small groups and even on individual retinalcells to generate focused phosphenes through devices implanted withinthe eye itself. This has sparked renewed interest in developing methodsand apparati to aid the visually impaired. Specifically, great efforthas been expended in the area of intraocular retinal prosthesis devicesin an effort to restore vision in cases where blindness is caused byphotoreceptor degenerative retinal diseases such as retinitis pigmentosaand age related macular degeneration which affect millions of peopleworldwide.

Neural tissue can be artificially stimulated and activated by prostheticdevices that pass pulses of electrical current through electrodes onsuch a device. The passage of current causes changes in electricalpotentials across retinal neuronal cell membranes, which can initiateretinal neuronal action potentials, which are the means of informationtransfer in the nervous system.

Based on this mechanism, it is possible to input information into thenervous system by coding the sensory information as a sequence ofelectrical pulses which are relayed to the nervous system via theprosthetic device. In this way, it is possible to provide artificialsensations including vision.

Some forms of blindness involve selective loss of the light sensitivetransducers of the retina. Other retinal neurons remain viable, however,and may be activated in the manner described above by placement of aprosthetic electrode device on the inner (toward the vitreous) retinalsurface (epiretinal). This placement must be mechanically stable,minimize the distance between the device electrodes and the retinalneurons, and avoid undue compression of the retinal neurons.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

Dawson and Radtke stimulated a cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 uAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

The Michelson '933 apparatus includes an array of photosensitive deviceson its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describesspike electrodes for neural stimulation. Each spike electrode piercesneural tissue for better electrical contact. U.S. Pat. No. 5,215,088 toNorman describes an array of spike electrodes for cortical stimulation.Each spike pierces cortical tissue for better electrical contact.

The art of implanting an intraocular prosthetic device to electricallystimulate the retina was advanced with the introduction of retinal tacksin retinal surgery. De Juan, et al. at Duke University Eye Centerinserted retinal tacks into retinas in an effort to reattach retinasthat had detached from the underlying choroid, which is the source ofblood supply for the outer retina and thus the photoreceptors. See,e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). Theseretinal tacks have proved to be biocompatible and remain embedded in theretina, and choroid/sciera, effectively pinning the retina against thechoroid and the posterior aspects of the globe. Retinal tacks are oneway to attach a retinal electrode array to the retina. U.S. Pat. No.5,109,844 to de Juan describes a flat electrode array placed against theretina for visual stimulation. U.S. Pat. No. 5,935,155 to Humayundescribes a retinal prosthesis for use with the flat retinal arraydescribed in de Juan.

SUMMARY

According to a first aspect of the present disclosure, an external coilassembly for an inductively coupled implant on the human or animal bodyis disclosed, comprising: a transmitting coil, adapted to transmitsignals to the implant; a first receiving coil, adapted to receivesignals from the implant, the first receiving coil exhibiting a firstcoupling coefficient with the transmitting coil; and a second receivingcoil, the second receiving coil exhibiting a second coupling coefficientwith the transmitting coil, wherein the first coupling coefficient issubstantially identical to the second coupling coefficient.

According to a second aspect of the present disclosure, an inductiveassembly adapted to communicate with an implant on the human or animalbody is disclosed, comprising: a transmitting inductor; a firstreceiving inductor, comprising a first coil, a first substrateassociated with the first coil, and a first metal shield connected withthe first substrate; and a second receiving inductor, comprising asecond coil, a second substrate associated with the second coil, and asecond metal shield connected with the second substrate, wherein thefirst receiving inductor and the second receiving inductor are locatedon different sides of the transmitting inductor and substantiallyequidistant from the transmitting inductor.

According to a third aspect of the present disclosure, an inductivetransceiver is disclosed, comprising: a transmitting coil; and areceiving coil, wherein a coupling coefficient between the transmittingcoil and the receiving coil is substantially equal to zero, and whereinthe inductive transceiver is adapted to interact with an implantimplanted in a human or animal body and is adapted to be locatedexternally to the human or animal body.

According to a fourth aspect of the present disclosure, an inductiveassembly adapted to be coupled with an implant on a human or animal bodyand to be located externally to the implant is disclosed, the assemblycomprising: a first inductor, the first inductor defining a first areainside the first inductor and a second area outside the first inductor;a second inductor located proximate to the first inductor, the secondinductor having a symmetrical shape comprised of a first second inductorregion and a second second inductor region the first second inductorregion defining a third area inside the first second inductor region,the second second inductor region defining a fourth area inside thesecond second inductor region, wherein intersection between the firstarea and the third area defines a first magnetic flux region,intersection between the first area and the fourth area defines a secondmagnetic flux region, intersection between the second area and the thirdarea defines a third magnetic flux region, intersection between thesecond area and the fourth area defines a fourth magnetic flux region,and wherein magnetic flux intensity through the first magnetic fluxregion and the second magnetic flux region is substantially equal andopposite to magnetic flux intensity through the second magnetic fluxregion and the third magnetic flux region.

According to a fifth aspect of the present disclosure, a method toimprove receiving sensitivity in an external coil assembly for aninductively coupled implant on the human or animal body is disclosed,wherein the external coil assembly comprises a transmitting coil and areceiving coil, the implant comprises an implant coil, the transmittingcoil allows transmission of a forward telemetry signal at a carrierfrequency to the implant, and the implant is adapted to send a backtelemetry signal to the external coil assembly, the method comprising:adjusting position of the receiving coil with respect to thetransmitting coil to reduce influence of a noise signal at the carrierfrequency received by the external coil assembly in addition to the backtelemetry signal.

According to a sixth aspect of the present disclosure, a visualprosthesis is disclosed, comprising: an image capture device convertinga visual image to a data stream; a video processing unit receiving thedata stream, applying filters to the data stream and providing aprocessed data stream; a transmitting coil, transmitting the processeddata stream; an implanted secondary coil receiving the processed datastream and transmitting operational data telemetry; implantedelectronics receiving the processed data stream from the implantedsecondary coil stimulating visual neural tissue and producing theoperational data telemetry; a first receiving coil, adapted to receivesignals from the implanted secondary coil, the first receiving coilexhibiting a first coupling coefficient with the transmitting coil; anda second receiving coil, the second receiving coil exhibiting a secondcoupling coefficient with the transmitting coil, wherein the firstcoupling coefficient is substantially identical to the second couplingcoefficient.

In accordance with the present disclosure, the back telemetry signalssent by the implant are reliably retrieved in the presence of a strongmagnetic field imposed by the PF carrier of the power transmitter,without increasing the complexity of the receiver circuits andcompromising the cosmetics of mechanical configuration of the externalcoils.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a first embodiment of an external coil assembly inaccordance with the present disclosure.

FIG. 2 shows an electrical diagram of the embodiment of FIG. 1.

FIG. 3 shows a second embodiment of the present disclosure.

FIGS. 4 and 5A-5C show sectional views referring to the secondembodiment.

FIGS. 6A-6C show a third embodiment of the present disclosure.

FIGS. 7A-7C show a fourth embodiment of the present disclosure, wherethe receiving coil has a differential configuration.

FIGS. 8A and 8B are magnetic flux diagrams helpful to understand theconcept expressed with reference to FIG. 7B.

FIGS. 9-11 show alternative differential embodiments of the receivingcoil of FIG. 7B.

DETAILED DESCRIPTION

FIG. 1 shows a first embodiment of an external coil assembly 10inductively coupled with an implant coil 20. The external coil assembly10 comprises inductors L1, L3 and L4. The implant coil 20 comprisesinductor L2. Throughout the present specification, the various inductorswill be described as coils, for exemplary purposes.

With reference to the external coil assembly 10, coil L1 represents atransmitting coil, and coils L3, L4 represent receiving coils.Transmitting coil L1 allows a forward telemetry (FT) signal to be sentto implant coil 20 or L2. Receiving coils L3 and L4 allow a backtelemetry (BT) signal to be received from the implant coil 20 or L2. Theconcept of FT signals and BT signals is known to the person skilled inthe art. See, for example, U.S. Pub. App. No. 2005/0288734 (VisualProsthesis with Operational Data Telemetry), incorporated herein byreference in its entirety. In accordance with this embodiment,transmitting coil L1 is located between receiving coils L3 and L4.Transmitting coil L1 is separated from receiving coils L3, L4 by meansof a dielectric, e.g. air. A possible distance between coil L1 and coilL4 or coil L1 and coil L3 is about 2 mm. In the embodiment of FIG. 1,coil L3 is identical to coil L4. Both coils L3 and L4 are placed at asame distance from L1. However, embodiments where L3 is different fromL4 can also be envisaged.

FIG. 2 shows an electrical diagram of the first embodiment of FIG 1. AnFT input signal amplified through power amplifier PA is fed totransmitting coil L1 and inductively received by implant coil L2.Implant coil L2 is part of an implant 30, further comprising atransceiver or stimulator 40. Implant 30 will not be described herewithin detail. A possible example of implant 30 can be found in U.S. Pub.App. No. 2005/0222624 (Retinal Prosthesis with Side Mounted InductiveCoil), incorporated herein by reference in its entirety. incorporatedherein by reference in its entirety. Among other functions, transceiver40 sends a back telemetry (BT) signal to coil L2 through driver 60. TheBT signal sent through coil L2 is inductively received by receiver coilsL3 and L4 and sent to a receiver circuit 70.

Magnetic coupling coefficients between the various pairs of coils areformed. The coupling coefficient measures the mutual inductance betweentwo inductors. The coupling coefficient between coils L1 and L2 isdefined as

${K_{12} = \frac{M_{12}}{\sqrt{L_{1}L_{2}}}},$

where M12 is the mutual inductance between coils L1 and L2. For twospiral type coils, the value of their coupling coefficient is determinedby their separation distance, coil dimensions, and their alignment. Inparticular, the coupling coefficient increases as the two coils movecloser, and decreases as they move farther.

On the external coil assembly side, coupling coefficient K13 defines themagnetic coupling between L1 and L3. Similarly, coupling coefficient K14defines the coupling between L1 and L4. When the external coil assembly10 interacts with the implant coil 20, further coupling coefficientsK12, K23 and K24 are defined, the meaning of which is identical to theone discussed above.

In accordance with the present disclosure K13 is made to besubstantially the same as K14, i.e. K13≈K14. In the present embodiment,coils L3 and L4 are arranged in a differential configuration in thecircuit. In particular, with reference to FIG. 2, the lower portion ofL3 is in-phase with the upper portion of L4, as shown by the position ofthe dots. Therefore, if the coils L3 and L4 are arranged so that theyreceive equal electromagnetic field strength from the L1), the net fieldstrength L3 and L4 receive from L1 is zero, thus obtaining the desiredcondition of rejecting the interferences from L1. In practicalrealization, the exact fulfillment of the K13=K14 requirement may not beachievable and what is relevant is that K13 is substantially equal toK14, i.e. K13≈K14. With “substantially equal” a condition is intendedwhere the direct influence of L1 on L3 and L4 when the BT signal isreceived from L2 is substantially reduced.

On the other hand, the coupling relation of the BT coils to the implantcoil L2 is different as to L1. By positioning L3 closer to L2 than L4,as shown in FIG. 1, K23 is made greater than K24, i.e. K23>K24. As aresult, the front coil L3 will receive a stronger field strength fromimplant coil L2 than the back coil L4. The net output produced by the BTcoils L3 and L4 from the implant coil is the difference between thesignals received by L3 and L4 individually.

The signals transmitted back from the implant 30 will include the BTsignals and reflected carrier signals. However, the reflected carriersignals coupled from L2 are much weaker in strength than the directtransmitting carrier signals coupled from L1. Therefore, by rejectingthe direct transmitting carrier signals from L1, the arrangement shownin FIGS. 1 and 2 provides the BT signals with a better signal-to-carriernoise ratio than using a single back telemetry receiving coil. Thereceiver circuit 70 will then condition and decode the BT signal.

FIG. 3 shows a further embodiment of the present disclosure, whereineach one of inductors L3, L4 can comprise: a coil layer 100 (or 110), aninsulator (or substrate) layer 120 (or 130), and an electrical shieldlayer 140 (or 150). This embodiment can be readily realized with adouble-layered printed circuit board (PCB) in which the coil and shieldare made of copper traces and the insulation is the PCB substrate. Asusual, L4 and L3 are separated from L1 by way of an insulator 160, e.g.air. The presence of the metallic shield layer shunts the straycapacitors around transmitting coil L1 so that the tuning condition isnot affected by the variation of the coil placement relative to thebody. It also prevents the displacement current produced by thetransmitting coil L1 from flowing through the human body. Incidentally,also the implant coil L2 can be shielded for the same purpose.

In order to reduce the loss of the transmitting power from L1 caused byEddy currents and thermal effect, thin traces or wires with goodconductivity such as copper can be used for the receiving coils L3 andL4 and also the electrical shielding. In practical applications, thephysical specifications of the coils, such as the coil dimensions,separations between the coils in the assembly, and coil configurations(turns, pitches, wire diameters etc.) can be optimized for therequirements of power and range of movement between coil L1 and theimplant coil L2.

FIG. 4 shows a top sectional view of an exemplary configuration oftransmitting inductor L1, comprising a coil 170 and insulator 180between the windings of the coil. Coil 170 can either be comprised ofsingle layer or multi-layer turns of conductors, such as copper. Forapplications demanding high power, multi-stranded Litz wires can be usedfor the conductors in coil 170 in order to reduce power loss due to skineffect.

FIG. 5A shows a top sectional view of an exemplary configuration ofinductor L3 or L4, comprising a coil 190, a substrate 200, and ametallic shield 210 (shown in dotted lines). FIG. 5B shows a partialview of the coil 190 and the substrate 200. FIG. 5C shows a partial viewof the metallic shield 210. The conductors (or traces) in 210 arearranged in such a way that they do not form any closed circles(circuits).

The electrical shielding can be connected to a low impedance point andstable electrical potential of the external assembly (e.g. the RF powerground) so that the stray capacitances are stabilized and the couplingor displacement path between the coil and the body is shunted. In orderto minimize the shielding effects to the magnetic field by the metalmaterials, low resistivity materials can be used, so that any Eddycurrent formed in the metal consumes a small amount of power. A meshtype structure with thin wires can also be used, without forming anyclosed circuit in the shield layer that acts like a coil to loopelectrical currents. This shield pattern is schematically indicated byreference numeral 210 in FIGS. 5A and 5C. The spaces between the tracesshown in FIG. 5C can be tuned close to the gap distance between the L1coil surface and the shield layer for a balance between good shieldingperformance and low degradation to the magnetic field.

FIGS. 6A-6C show a further embodiment of the present disclosure, wherethe external coil assembly 10 is provided with one transmitting inductorL1 and one receiving inductor L3, as shown in FIG. 6A. The electricalbehavior of the embodiment of FIG. 6A can be understood with referenceto FIG. 6C, which is conceptually similar to FIG. 2. In the embodimentat issue, a single coupling coefficient is formed on the external coilassembly side, i.e. K13, which defines the coupling between L1 and L3.When the external coil assembly 10 interacts with implant coil L2,further coupling coefficients K12 and K23 are defined.

In accordance with this additional embodiment, K13 is made as proximateas possible to zero. This can be obtained, for example, by displacing L3with respect to L1, when seen from the top, as shown in FIG. 6B. Inparticular, L1, when seen from the top or from the bottom, defines abound internal (substantially circular in the embodiment of FIG. 6B)area and an unbound external area. Similarly, L3 also defines a boundinternal area. The applicant has noted that K13 can be reduced to zeroby displacing L3 with respect to L1 so that the internal area defined byL3 is spatially associated both with the internal area defined by L1 andthe external area defined by L1. In particular, K13 can be reduced tozero when the magnetic flux B going through dotted area 250 has anintensity which is equal to the intensity of the magnetic flux B goingthrough x'd area 260.

FIGS. 7A-7C show another embodiment of the present disclosure, where theexternal coil assembly 10 is provided with receiving inductors L3, L4arranged on the same side of the transmitting inductor L1. The inductorsL3, L4 can be seen as two distinct inductors or as a single inductorcomprising portions L3, L4. The electrical behavior of the embodiment ofFIG. 7A can be understood with reference to FIG. 7C, which isconceptually similar to FIGS. 4 and 6C. In the embodiment at issue,coupling coefficients K13 and K14 are formed on the external coilassembly side and coupling coefficients K12, K23 and K24 are formed whenthe external coil assembly 10 interacts with implant coil L2.

Given that both inductors L3 and L4 are located on the same side ofinductor L1, the in-phase arrangement of L3 and L4 is different fromthat shown in FIG. 2, as shown by the position of the dots in FIG. 7C.Therefore, in this case, minimization of the combined couplingcoefficient inside arrangement 10 is obtained by designing L3 and L4 sothat K13=−K14. This can be obtained, for example, by displacing L3 andL4 with respect to L1, when seen from the top, as shown in FIG. 7B. Eachof L3 and L4, when seen from the top or the bottom, defines an internalarea. The applicant has noted that K13 can be made equal and opposite toK14 by displacing L3, L4 with respect to L1 so that the internal areasdefined by each of L3 and L4 are spatially associated both with theinternal area and the external area defined by L1. In particular,K13+K14 can be made equal to zero when the intensity of the magneticflux B going through dotted areas 270, 280 is equal to the intensity ofthe magnetic flux B going through x'd areas 290 and 300.

In other words, the magnetic field created by L1 is distributed in sucha way that a) the direction of the field enclosed by the coil turns isopposite to the direction of the field surrounding them and b) theintensity of the field enclosed by the coil turns is equal to theintensity of the field surrounding the coil turns. A qualitativeexplanation of this concepts is shown in FIGS. 8A and 8B, where FIG. 8Ashows a cross sectional view of the magnetic field distribution in thecase at issue, and FIG. 8B shows a top view thereof. (+) field lines areoutward field lines, while (−) field lines are inward field lines. Thenet magnetic fluxes passing through the receiving coils L3, L4 areminimized to zero, at which condition the effective coupling between theexternal transmitting coil L1 and the external receiving coils L3, L4 isnegligent. In this way, the effect of the power carrier during receptionis minimized while, at the same time, the forward coupling between theimplant coil L2 and the external receiving coils L3, L4 still follows asize and distance relationship.

To maximize the receiving sensitivity, the receiving coil or coilsshould be tuned to the carrier frequency of the BT signal. Thepositioning of the receiving coil relative to the transmitting coil canbe tuned by driving the transmitting coil with the transmitting coilwith the power carrier frequency and monitoring the receiving signalstrength of the same frequency at the receiving coil in the same time.The optimal position is where the signal strength is the lowest. In caseof an inductively powered implant, the power carrier component receivedby the external receiver coil is composed of two parts: a partoriginating from the transmitting coil L1 and a part reflected from theimplant coil L2 with a phase shift. Therefore, the position of thereceiver coil L3 or L3, L4 should be tuned in the presence of theimplant.

The embodiment shown in FIGS. 7A-7C is a differential embodiment.Similar embodiments are shown in FIGS. 9-11. The person skilled in theart will understand that those embodiments are for exemplary purposesonly and that similar or different embodiments can be envisaged. In theembodiments of FIGS. 9-11, the windings of the wires of the receivingcoil are not shown, for the sake of clarity. In the embodiment of FIG.9, the receiving coil L3 is comprised of two substantially circularportions connected by an elongated portion. In FIG. 10, the receivingcoil L3 is comprised of two substantially mushroom-shaped portionsconnected by an elongated portion. In FIG. 11, the receiving coil L3 iscomprised of four substantially

While several illustrative embodiments of the invention have been shownand described in the above description, numerous variations andalternative embodiments will occur to those skilled in the art. Suchvariations and alternative embodiments are contemplated, and can be madewithout departing from the scope of the invention as defined in theappended claims.

1. An inductive assembly adapted to communicate with an implant on thehuman or animal body, comprising: a transmitting inductor; a firstreceiving inductor, comprising a first coil, a first substrateassociated with the first coil, and a first metal shield connected withthe first substrate; and a second receiving inductor, comprising asecond coil, a second substrate associated with the second coil, and asecond metal shield connected with the second substrate, wherein thefirst receiving inductor and the second receiving inductor are locatedon different sides of the transmitting inductor and substantiallyequidistant from the transmitting inductor.
 2. The inductive assembly ofclaim 1, wherein the first substrate and the second substrate are a PCBsubstrate.
 3. The inductive assembly of claim 2, wherein the PCBsubstrate is a double-layered PCB.
 4. The inductive assembly of claim 1,wherein the first metal shield and the second metal shield are made of amaterial selected from the group consisting of traces and wires.
 5. Theinductive assembly of claim 1, wherein the transmitting inductor, firstreceiving inductor and second receiving inductor are separated therefromby way of an insulator.
 6. The coil assembly of claim 5, wherein theinsulator is air.
 7. An inductive transceiver comprising: a transmittingcoil; and a receiving coil, wherein a coupling coefficient between thetransmitting coil and the receiving coil is substantially equal to zero,and wherein the inductive transceiver is adapted to interact with animplant implanted in a human or animal body and is adapted to be locatedexternally to the human or animal body.
 8. The inductive transceiver ofclaim 7, wherein: the receiving coil is displaced with respect to thetransmitting coil in a view from the top or the bottom of thetransmitting coil and the receiving coil; the transmitting coil definesa first area internal to the transmitting coil and a second areaexternal to the transmitting coil; the receiving coil defines a thirdarea internal to the receiving coil; and the third area is located onand above a portion of the first area and a portion of the second area.9. An inductive assembly adapted to be coupled with an implant on ahuman or animal body and to be located externally to the implant, theassembly comprising: a first inductor, the first inductor defining afirst area inside the first inductor and a second area outside the firstinductor; a second inductor located proximate to the first inductor, thesecond inductor having a symmetrical shape comprised of a first secondinductor region and a second second inductor region, the first secondinductor region defining a third area inside the first second inductorregion, the second second inductor region defining a fourth area insidethe second second inductor region, wherein intersection between thefirst area and the third area defines a first magnetic flux region,intersection between the first area and the fourth area defines a secondmagnetic flux region, intersection between the second area and the thirdarea defines a third magnetic flux region, intersection between thesecond area and the fourth area defines a fourth magnetic flux region,and wherein magnetic flux intensity through the first magnetic fluxregion and the second magnetic flux region is substantially equal andopposite to magnetic flux intensity through the second magnetic fluxregion and the third magnetic flux region.
 10. The inductive assembly ofclaim 9, wherein the first second inductor region and the second secondinductor region are circularly shaped.
 11. The inductive assembly ofclaim 9, wherein the first second inductor region and the second secondinductor region are mushroom shaped.
 12. The inductive assembly of claim9, wherein the second inductor further comprises a third second inductorregion and a fourth second inductor region.